Question

what is focal plane ?¿​

Answer 1

A plane drawn perpendicular to the principal axis and passing through the principal focus.

Answer 2

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ᴡʜᴀᴛ ɪs ғᴏᴄᴀʟ ᴘʟᴀɴᴇ?

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• the plane through the focus perpendicular to the axis of a mirror or lens.
• In camera design, a focal-plane shutter is a type of photographic shutter that is positioned immediately in front of the focal plane of the camera, that is, right in front of the photographic film or image sensor.